Portal.imageUrl returns a ghost URL when the id is undefined

Bugs
1 
    var backgroundImage = execute('portal.imageUrl', {
        id: xeonConfig.bannerBackground,
        format: 'jpg'
    });
    xeon.log(xeonConfig.bannerBackground);
    xeon.log(backgroundImage);

In the above code, there are times when the value of “xeonConfig.bannerBackground” is undefined. When that happens, the result should be null. But it instead returns the URL for a ghost content.

The log returns:
undefined
“/admin/portal/preview/draft/xeon/_/image/f5f0376c-e2d6-4016-8d87-055a5c91f424/xeon.jpg”

Also, when I tried putting that URL into the browser, it gets and error saying the content is not an image.

This happens in version 5.2.0.